Dual Bridge PS - Does Phase of Secondary Matter?

[lgreen]

I am wiring up my dual bridge power supply. One bridge for + rail and another bridge for the - rail.

Just like the first watt power supplies and chipamp power supplies.
Example, F1 manual, go to page 9. Link.
Example, chipamp.com PS, go to page 4 - Link.

Or just look at this (from chipamp.com).




Note that none of these schematics have the little dots indicating secondary polarity.

Question: Does it matter that the top and bottom secondaries are in-phase or out of phase with each other? If so which is the way to do it (assume in phase but I could be wrong).

[stratus46]

Originally Posted by lgreen

I am wiring up my dual bridge power supply. One bridge for + rail and another bridge for the - rail.

Just like the first watt power supplies and chipamp power supplies.
Example, F1 manual, go to page 9. Link.
Example, chipamp.com PS, go to page 4 - Link.

Or just look at this (from chipamp.com).




Note that none of these schematics have the little dots indicating secondary polarity.

Question: Does it matter that the top and bottom secondaries are in-phase or out of phase with each other? If so which is the way to do it (assume in phase but I could be wrong).

I can't imagine how it could matter. It just defines which diodes are conducting on a particular half cycle. My question is how is this better than wiring the secondaries in series and using 1 bridge instead of 2 ? One minor downside is you lose .7 Volts because of the extra diodes in the path in this scheme.

G²

[Xoc1]

Apart from the increased voltage drop from using 2 separate bridge rectifiers, the only real advantage is reducing the thermal stress on the bridge rectifiers when used in high power amplifiers.

[martinbls]

Well, I asked myself just the same question when I build my chipamp, and so I tried out both versions, in phase and out of phase. And the difference was: none! Neither in sound quality nor regarding the general function of the amp. So I would guess it really doesn't matter.

Regards!
martin

[lgreen]

Originally Posted by stratus46

I can't imagine how it could matter. It just defines which diodes are conducting on a particular half cycle. My question is how is this better than wiring the secondaries in series and using 1 bridge instead of 2 ? One minor downside is you lose .7 Volts because of the extra diodes in the path in this scheme.

G²

This Article on tnt-audio.com says two bridges are good. I just did it that way cause I had a 2 bridge PCB, not for any real techie reason.

Note that even here the phase of each secondary is not mentioned. Leaving it to the reader to be confused!


Lastly, Figure 4 illustrates a serious power supply. For a start, we see that each half of the supply has its own full wave bridge rectifier. This allows for significantly improved rectification, as well as offering the designer greatly increased power handling capabilities, since two rectifiers now share the work load of one. This approach is quite common in American High End units, and has during the last several years begun to trickle downwards, into higher middle class units. A welcome change indeed.

But the real reason why this is done is twofold. First, this allows for much better channel separation, since each supply line is independent, and is therefore much less likely to transmit signal from one channel to the other. The other reason is essentially the same, but with regard to ground planes - this method produces more ground planes, but avoids mixing them, thus once again minimizing possibilities of crosstalk and improving our signal to noise ratios. For this to be so, one also needs dedicated transformer secondary windings, for a stereo amp a total of four, rather than the classic two. Obviously, while good and with many advantages, this is a considerably more expensive design.

[infinia]

Hi
The first diagrams posted are correct but not this last one.
The advantage of dual rectifiers is clean and quiet GROUNDING full stop. This is best configured by using a star ground. This star is at the junction of both returns at the lowest ripple point ie at the cap outputs. Not as shown in this last figure> The draw back is you have 2 diode drops instead of one. Double bridge rectifiers are best ONLY If you have dual secondaries.

Nothing is gained by using double bridges for a common center tapped XFMR, then using one bridge carefully implemented is best.

[lgreen]

Originally Posted by infinia

Hi
The first diagrams posted are correct but not this last one.
The advantage of dual rectifiers is clean and quiet GROUNDING full stop. This is best configured by using a star ground. This star is at the junction of both returns at the lowest ripple point ie at the cap outputs. Not as shown in this last figure> The draw back is you have 2 diode drops instead of one. Double bridge rectifiers are best ONLY If you have dual secondaries.

Nothing is gained by using double bridges for a common center tapped XFMR, then using one bridge carefully implemented is best.

OK, that is what I thought too. But what about the relative phase(s) of the secondaries? Does it matter if they are in phase or out of phase or not?

[infinia]

Sorry I thought that had been answered, No phase doesnt matter for dual secondary dual bridge.
The diodes steer it in the right direction before they are tied together

[Sch3mat1c]

What silliness is this?

Originally Posted by lgreen

Lastly, Figure 4 illustrates a serious power supply. For a start, we see that each half of the supply has its own full wave bridge rectifier. This allows for significantly improved rectification, as well as offering the designer greatly increased power handling capabilities, since two rectifiers now share the work load of one.

1. Rectification isn't improved, it's impaired. The voltage drop is *doubled*.
2. The "duh" answer: increase power handling by using a properly rated bridge. They make single unit FWB's good for well over 100A, or you can buy individual diodes (stud, module or puck style), which are easier to cool and are available into the kiloamp range.

This approach is quite common in American High End units, and has during the last several years begun to trickle downwards, into higher middle class units. A welcome change indeed.

3. This is the real reason -- "because they did it". Audiophoolery, as a cultural phenomenon, cares not for rational thought. (So why even bother wasting my time, right?)

But the real reason why this is done is twofold. First, this allows for much better channel separation, since each supply line is independent, and is therefore much less likely to transmit signal from one channel to the other.

4. WTF? The channels are on the same +/- rails! They aren't on positive only and negative only!

The proper solution is to connect the secondaries in series (the phase is obvious to check and nonfatal if wrong -- if the end-to-end voltage is near 0V, it's backwards) and use one FWB. The CT between windings comes straight out as GND.

Tim

[Elvee]

Sch3mat1c is right: it is indeed a load of nonsense.
In addition, the dual bridge scheme creates more paths for RF modulation by the diodes, and more sources of reverse recovery noise.
It also impairs the grounding, because the transformers windings have no direct galvanic connection to the ground, and cannot act as a partial shield against mains-borne interferences.
Finally, in the zero-crossing region of the mains waveform, the windings are left completely floating, high-impedance.